Answer:
4 lb
Step-by-step explanation:
Subtracting 4 lb from 18 lb yields 14 lb, the weight of the backpack without math book: 18 lb - 4 lb = 14 lb
The math book weighs 4 lb.
His dog ate 1/2 of his collection, this means that there are only 33 left. If I multiply 33x2, I will get 66. Therefore, Fred started with 66 cards.
(If you’re not counting the cards he purchased, then Fred would have 59 cards.)